U.S. patent number 10,328,725 [Application Number 15/718,008] was granted by the patent office on 2019-06-25 for device for detecting a position of a printing material transported in a printing machine.
This patent grant is currently assigned to Heidelberger Druckmaschinen AG. The grantee listed for this patent is HEIDELBERGER DRUCKMASCHINEN AG. Invention is credited to Thomas Goebel, Andreas Henn, Wolfgang Kabus, Stefan Knauf, Olaf Lorenz, Stefan Muench, Stefan Mutschall, Steffen Neeb, Nicklas Raymond Norrick, Juergen Ritz, Thomas Schmidt, Stephanie Weinig-Kress.
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United States Patent |
10,328,725 |
Knauf , et al. |
June 25, 2019 |
Device for detecting a position of a printing material transported
in a printing machine
Abstract
A device detects at least one position of at least a part of a
printing material while the printing material is transported in a
printing machine. The device includes an optical sensor for
establishing a distance between a printing machine component and
the printing material. The distance established by the optical
sensor is temperature-compensated by a computer.
Inventors: |
Knauf; Stefan (Heidelberg,
DE), Henn; Andreas (Neckargemuend, DE),
Ritz; Juergen (Dielheim, DE), Lorenz; Olaf
(Mutterstadt, DE), Schmidt; Thomas (Heidelberg,
DE), Muench; Stefan (Heidelberg, DE),
Goebel; Thomas (Muehlhausen, DE), Kabus; Wolfgang
(Schriesheim, DE), Weinig-Kress; Stephanie
(Bruchsal-Heidelsheim, DE), Mutschall; Stefan
(Oestringen, DE), Norrick; Nicklas Raymond
(Eppelheim, DE), Neeb; Steffen (Bensheim,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
HEIDELBERGER DRUCKMASCHINEN AG |
Heidelberg |
N/A |
DE |
|
|
Assignee: |
Heidelberger Druckmaschinen AG
(Heidelberg, DE)
|
Family
ID: |
61623391 |
Appl.
No.: |
15/718,008 |
Filed: |
September 28, 2017 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20180093501 A1 |
Apr 5, 2018 |
|
Foreign Application Priority Data
|
|
|
|
|
Sep 30, 2016 [DE] |
|
|
10 2016 219 026 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B41J
2/1408 (20130101); B41J 11/0095 (20130101); G01J
5/06 (20130101); G06K 15/1219 (20130101); G01J
2005/068 (20130101) |
Current International
Class: |
B41J
2/14 (20060101); G06K 15/12 (20060101); B41J
11/00 (20060101); G01J 5/06 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Huffman; Julian D
Attorney, Agent or Firm: Greenberg; Laurence A. Stemer;
Werner H. Locher; Ralph E.
Claims
The invention claimed is:
1. A device for detecting at least one position of at least a part
of a printing material while the printing material is transported
in a printing machine, the device comprising: an optical sensor for
establishing a distance between a printing machine component and
the printing material; and a computer for temperature-compensating
the distance established by said optical sensor; said computer
saving an intensity pattern of said optical sensor on said
computer, and said intensity pattern representing a measurement
uninfluenced by external temperatures; said computer comparing an
intensity pattern established by said optical sensor under thermal
influences and said saved intensity pattern without thermal
influence; and said computer calculating said thermal influence and
compensating for said thermal influence in a computational way
based on a deviation between said two patterns.
2. The device according to claim 1, which further comprises: a
light source emitting light beams in a beam path in a direction
toward said optical sensor; at least parts of the printing material
being located in said beam path between said light source and said
optical sensor; and said optical sensor being a CCD line sensor
including a plurality of CCD elements.
3. The device according to claim 2, wherein said light source
includes a lens to widen an illumination in parallel.
4. The device according to claim 2, wherein said light source is
dot-shaped.
5. The device according to claim 2, which further comprises a cover
plate disposed between said light source and said optical
sensor.
6. The device according to claim 1, wherein said computer compares
a height difference between a first local maximum of said saved
intensity pattern and a first local maximum of said measured
intensity pattern in said comparison of said intensity patterns
carried out on said computer.
7. The device according to claim 1, which further comprises a
temperature control device for controlling a temperature of at
least parts of the printing machine in a region of a measuring
process.
8. The device according to claim 1, wherein said computer switches
the printing machine off when a measured distance between said
optical sensor and the printing material exceeds a predefined
value.
9. The device according to claim 8, wherein said predefined value
is a temperature-dependent switch-off threshold.
10. A device for detecting at least one position of at least a part
of a printing material while the printing material is transported
in a printing machine, the device comprising: an optical sensor for
establishing a distance between a printing machine component and
the printing material; a computer for temperature-compensating the
distance established by said optical sensor, said computer saving
an intensity pattern of said optical sensor on said computer, and
said intensity pattern representing a measurement uninfluenced by
external temperatures; and at least one temperature sensor for
measuring a temperature of grippers of the printing machine for
transporting sheet-shaped printing materials, said at least one
temperature sensor transmitting said measured temperature to said
computer.
Description
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit, under 35 U.S.C. .sctn. 119, of
German Patent Application DE 10 2016 219 026.1, filed Sep. 30,
2016; the prior application is herewith incorporated by reference
in its entirety.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a device, including a computer,
for detecting at least one position of at least a part of a
printing material while the printing material is transported in a
printing machine. The device includes an optical sensor for
establishing a distance between a printing machine component and
the printing material.
Devices of that general kind for detecting at least one position of
at least a part of a printing material are used in digital printing
machines, in particular inkjet printing machines, to ensure that
the printing material is transported past the print heads at a safe
distance therefrom. The print heads of inkjet printing machines are
very delicate and may be damaged by contact with the printing
material. Thus, it is mandatory that the printing material in
inkjet printing machines maintain a defined distance from the
inkjet print heads. However, since the distance between the
printing material and the inkjet print heads is very short,
amounting to mere fractions of a millimeter, the measuring device
for establishing the position of the printing material needs to
operate with a high degree of accuracy. If the distance is not
established correctly and the sheet-shaped printing material is
actually closer to the inkjet print head, damage may occur.
However, if the actual distance between the printing material and
the print head is greater than the measured distance and still
sufficient, the inkjet printing machine will be unnecessarily
stopped, reducing the overall productivity of the machine. The
device for detecting the position of the printing material
therefore needs to operate with great accuracy and needs to be
immune to external influences.
At present, the sensors for monitoring the distance between the
printing material and the print head in an inkjet printing machine
are light barriers that monitor a line parallel to a jetting
cylinder to recognize when the sheet on the jetting cylinder moves
too far away from the jetting cylinder and threatens to contact the
print heads. The light barrier uses a dot-shaped light source and a
dot-shaped receiver. A problem of that way of monitoring the
distance between the printing material and the print heads or
rather between the printing material and the jetting cylinder is
that a correct measuring of the distance is dependent on thermal
influences. Different temperature layerings, i.e. regions of
different temperatures in terms of printing material, jetting
cylinder, ambient air, etc. cause the light of the light barrier to
be deflected. That deflection then causes the distance to be
perceived as too great, causing the printing process to be stopped
and affecting the performance of the inkjet printing machine
because the print heads need to be lifted for safety reasons and
the printing process is disrupted.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a device
for detecting at least one position of at least a part of a
printing material while the printing material is transported in a
printing machine, which overcomes the hereinafore-mentioned
disadvantages of the heretofore-known devices of this general type
and which is capable of detecting the position of at least a part
of a printing material even if there are different temperatures at
the printing material, the jetting cylinder, the grippers, etc. or
in the ambient air in order to ensure reliable operation of the
printing machine without any unnecessary machine stops for safety
reasons while at the same time avoiding damage to the print
heads.
With the foregoing and other objects in view there is provided, in
accordance with the invention, a device for detecting at least one
position of at least a part of a printing material while the
printing material is transported in a printing machine. The device
comprises an optical sensor for establishing a distance between a
printing machine component and the printing material, and a
computer for temperature-compensating the distance established by
the optical sensor.
In accordance with the invention, it is envisaged that the distance
detected by the optical sensor is temperature-compensated by using
the computer. This means that temperature-related deviations during
the establishment of the distance between the printing material and
a machine component such as the print head or jetting cylinder are
compensated for in a computational way, allowing thermal influences
to be eliminated as far as possible on the computer. For this
purpose, the measured distance values are subjected to temperature
compensation on the computer before they are processed to control
the printing machine. The temperature compensation carried out by
the computer factors in temperature-related measurement deviations
by using a model. This model is saved in the form of software on
the computer. Based on specific characteristics of the measuring
process, the model recognizes the thermal influences, allowing the
thermal influence to be detected as a disturbing quantity and the
measurements to be corrected by the disturbing quantity. This
ensures that the correct actual distance, uninfluenced by
measurement errors, is used to control the printing machine. In
this way, the productivity of the printing machine is increased
while ensuring that the print heads are protected against contact
with the printing material. In accordance with the present
invention, the correction may be made in an exclusively
computational way by software on the computer. No hardware in terms
of the optical sensor needs to be adapted and known light barriers
may continue to be used.
In accordance with a first embodiment of the invention, it is
envisaged that the optical sensor is a CCD line sensor that
includes a plurality of CCD elements and the device includes a
light source emitting light beams in the direction of the optical
sensor, with at least parts of the printing material located in the
beam path between the light source and the optical sensor. In this
case, a CCD line sensor is mounted on one side of the jetting
cylinder in the printing machine and a light source is present on
the opposite side. Together, the CCD line sensor and the light
source form a light barrier. Without thermal influences, the light
beams extend in a direction parallel to the jetting cylinder and
reach the CCD line sensor on the shortest path without deflection.
The light beams are disposed in such a way that they are at the
required safe distance from the inkjet print head. Alternatively, a
partial shadowing may be envisaged, involving a known number of
beams that are always shadowed. This known partial shadowing is
then factored-in in a corresponding way when the light barrier is
evaluated. As soon as at least parts of the printing material
interrupt the beam path, it is to be assumed that the minimum
distance between the light beam and the print head has been
violated because at least a part of the printing material has
entered the danger zone and has lifted too far off the jetting
cylinder. In order to prevent damage, the computer will then either
stop the machine completely or use a mechanism to lift the print
heads to avoid contact with the printing material. However,
different temperature layerings caused by temperature differences
between jetting cylinder, printing material, and ambient air as
well as grippers that guide the printing material, may deflect the
light beam in an upward or downward direction. If the light beam is
deflected in an upward direction, an insufficient distance from the
print head located above the jetting cylinder is detected too late,
resulting in a risk of damage. If the light beam is deflected in a
downward direction, a penetration of the safety zone is wrongly
detected even though there is still enough distance between the
printing material and the print head. These two errors are
corrected by the computer in the temperature compensation process,
preventing a wrong reaction in the printing machine control.
In a further embodiment of the invention it is envisaged that an
intensity pattern of the optical sensor is saved on the computer,
the intensity pattern representing a measurement without any
external thermal influences. In this case, an evaluation of the
interaction between the CCD elements and the light source of the
optical sensor is made without any thermal influences. This means
that printing material, ambient air, grippers and jetting cylinder
all have the same temperature and the light beams reach the CCD
line sensor without deflection. The resultant intensity pattern is
saved on the computer as a correct measurement and is later used as
a reference for distance measurements during operation if
deviations occur due to temperature layerings. The temperature
layerings cause the light beam to be deflected in an upward or
downward direction, resulting in different intensity patterns due
to the thermal influences.
In accordance with the invention, it is furthermore envisaged that
the computer compares the intensity patterns established by the
optical sensor under thermal influences and the saved intensity
pattern without thermal influence and, based on the deviation
between the two patterns, calculates the thermal influence and
compensates for the thermal influence in a computational way. The
comparison between the measured intensity patterns and the saved
intensity pattern allows the computer to detect temperature
deviations because different temperature deviations result in
different intensity patterns. Thus, the computer may use the
intensity signal to extract the temperature information required
for a correction and may take suitable compensatory measures. This
compensation may, for instance, be carried out on the basis of a
table that is likewise saved on the computer and indicates positive
and negative correction values in terms of the printing material
distance in accordance with the measured temperature information.
These correction values are then added to the measured distance
value to calculate the actual distance by using the computer.
In accordance with a further embodiment of the invention, it is
envisaged that the height difference between the first local
maximum of the saved intensity pattern and the first local maximum
of the measured intensity pattern are compared in the comparison
when the computer compares the intensity patterns. Prior to the
comparison between the local maximums the intensity curves are
filtered or smoothed on the computer if necessary. The difference
between the first local maximums is clearly positive in an
uninfluenced case but negative in the case of a cold surface. In
this way, a temperature deviation may be detected and suitable
temperature compensation may be achieved for the signal.
In a further embodiment of the present invention it is envisaged
that the light source includes a lens to widen the illumination in
parallel. The lens creates parallel beams from a dot-shaped light
source. The light beams accordingly hit the CCD line sensor in
parallel. In this way, due to the plurality of parallel light
beams, a large region between the jetting cylinder and the print
head may be monitored for printing material distance
violations.
In an alternative embodiment of the present invention it is
envisaged that the light source is dot-shaped. In this case, there
is no parallel widening of the illumination but characteristic
intensity curves are created on the CCD line sensor
nonetheless.
Advantageously it is also envisaged that the temperature of at
least parts of the printing machine in the region of the measuring
operation are controlled by a temperature control device. Since
temperature compensation by using the computer is limited to a few
degrees Celsius, an additional temperature control device may be
provided to control the temperature of at least some parts of the
printing machine or printing material in the region of the
measuring operation in order to reduce the measurement deviations.
Targeted temperature control on printing material, jetting
cylinder, grippers, or ambient air in the region of the measuring
operation may minimize temperature differences, reducing the
measurement deviations in the distance measurement to a
considerable extent. This reduces measurement deviations in advance
and thus temperature compensation only needs to be implemented over
a small range. However, the provision of a suitable temperature
control device is complex in terms of construction and a
temperature control device will always require an energy
supply.
In a further embodiment of the invention it is envisaged that the
computer switches the printing machine off when the measured
distance between the optical sensor and the printing material
exceeds a predefined value. Switching off the printing machine
prevents collisions between the printing material and the print
heads. However, the printing machine does not need to be completely
switched off. It is sufficient if the printing process is switched
off, for instance by lifting the print heads, and if a printing
material that is not at the required safe distance is not printed.
Switching off the printing machine in this context simply means
switching off the printing process for a printing material.
In a further embodiment of the present invention it is envisaged
that the switch-off threshold is temperature-dependent. In this
case, there is no compensation of the distance measuring
temperature. Instead, the switch-off threshold is lowered or
increased as a function of the temperature deviation established by
the intensity measurement. This process in the end likewise amounts
to compensated distance measurement. A modified switch-off
threshold as a function of the temperature thus presents an
alternative to correcting the measured distance.
In a further embodiment of the present invention it is envisaged
that a cover plate is provided between the light source and the
receiver. The use of the cover plate may suppress the spatial
region of the steep temperature gradients. This reduces the
influence of the temperature deviation. However, the position of
the cover plate depends on the thickness of the printing material
and thus needs to be adjusted as a function of the printing
material thickness. This requires a manual or automated adjustment
of the cover plate.
Advantageously, it is furthermore envisaged that the printing
machine includes grippers for transporting sheet-shaped printing
material and at least one temperature sensor for sensing the
temperature of the grippers and forwarding it to the computer. The
computer may use the temperature of the grippers sensed by one or
more temperature sensors to establish the temperature-dependent
modification of the switch-off threshold on the computer. Then the
computer may correct the switch-off threshold as a function of the
sensed gripper temperature. In a similar way, the temperature of
the jetting cylinder and of the ambient air may be sensed.
Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in a device for detecting a position of a printing
material transported in a printing machine, it is nevertheless not
intended to be limited to the details shown, since various
modifications and structural changes may be made therein without
departing from the spirit of the invention and within the scope and
range of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be
best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
FIG. 1 is a diagrammatic view of a portion of a digital printing
machine having fundamental structures illustrating a measuring
principle of a distance measurement when bad sheets occur;
FIG. 2 is a side-elevational view illustrating an ideal intensity
pattern without thermal influences on a CCD line;
FIG. 3 is a diagram illustrating an actual intensity signal without
thermal influences on a CCD sensor;
FIG. 4 is a view similar to FIG. 2 illustrating a deflection of a
light beam by temperature layering effects;
FIG. 5 is another view similar to FIGS. 2 and 4 illustrating a
deflection of the light beam due to increased gripper
temperatures;
FIG. 5A is a diagram illustrating an intensity signal that has been
influenced by the increased gripper temperature; and
FIG. 6 is a further view similar to FIGS. 2, 4 and 5 illustrating a
configuration including a cover plate in a region of temperature
gradients.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the figures of the drawings in detail and first,
particularly, to FIG. 1 thereof, there are seen fundamental
structures for distance detection using a CCD line sensor 6 and an
emitter 2 in a digital printing machine 1. By way of example, FIG.
1 shows a measuring object 7, which is a sheet 9 shown in FIG. 4,
in the digital printing machine 1. For safety reasons, the distance
between the sheet 9 and non-illustrated print heads in the digital
printing machine 1 always needs to be large enough to avoid contact
between the print heads and the sheet 9 in order to avoid damage to
the print heads. The CCD line sensor 6 in FIG. 1 is integrated in a
receiver 5, which additionally includes a measuring aperture 8 that
allows light beams 11 (also shown in FIGS. 2, 4, 5 and 6) emitted
by the emitter 2 to reach the CCD line sensor 6. The emitter 2 is
substantially formed of a light source in the form of a laser diode
4 and a lens 3, which widens the beam path of the laser diode 4 and
generates parallel light beams emitted in the direction of the
receiver 5. When a measuring object 7 is located in the beam path,
corresponding CCD elements on the CCD line sensor 6 are shadowed,
allowing the width of the measuring object 7 and the position of
the latter to be determined in FIG. 1. This measuring principle is
used to determine the distance between the sheet 9 and the print
heads in the printing machine 1.
FIG. 2 illustrates the implementation of the measuring principle of
FIG. 1. Like FIG. 1, an emitter 2 is disposed on the left-hand
side. The emitter 2 emits parallel light beams 11 that are received
by a CCD line sensor 6 on the opposite side of the digital printing
machine 1. The light beams 11 are emitted in a direction parallel
to a jetting cylinder 17, which transports the printing material 9
during the printing operation. The jetting cylinder 17 extends from
the drive side to the operator side of the printing machine, which
is the reason why the emitter 2 and the receiver including the CCD
line sensor 6 are likewise respectively suitably disposed on the
drive and operator sides of the printing machine. The CCD line
sensor 6 is furthermore connected to a computer 15, which may
simultaneously be the control unit of the digital printing machine
1. In this way, the computer 15 may evaluate the light beams 11
received by the CCD line sensor 6. FIG. 2 shows that the jetting
cylinder 17 shadows a part of the light beams 11. The computer 15
knows about this shadowing effect and does not react until further
light beams 11 are interrupted in addition to the known partial
shadowing. The partial shadowing is expedient because it has been
found that the emitter 2 and the sensor 6 make more reliable
evaluations in the middle range. Thus, the marginal regions are
eliminated by the partial shadowing. In addition, an ideal
intensity signal 10 is shown to the right of the line sensor 6 in
FIG. 2. This ideal intensity signal is without any thermal
influences and with a theoretical, infinite resolution.
The real intensity signal is shown in FIG. 3. This real intensity
signal is also not influenced by thermal effects but is based on an
actual resolution of a limited number of CCD elements in the line
sensor 6. The number of the respective CCD element is indicated on
the X axis and the intensity (in percentages) is indicated on the Y
axis. Every CCD element measures an intensity between 0 and 100%;
the intersection of the line parallel to the x axis at an intensity
of 12.5% and the intensity curve indicates the position of the
sheet edge. The edge position I is thus located approximately at
CCD element 275. Based thereon, the computer 15 may calculate the
distance of the edge and the position of the edge of the sheet 9.
In this way, the computer 15 receives information on the distance
between the sheet 9 and the print head or rather the jetting
cylinder 17 disposed to be parallel thereto, and whether or not the
print heads are at risk because the minimum distance is potentially
not met.
In practice, the development of the intensity signal 10 on the CCD
line sensor 6 is highly influenced by temperature layerings during
the measuring process. The effect of this temperature layering is
shown in FIG. 4. The print sheet 9 has a temperature
T.sub.B=25.degree. C. The jetting cylinder 17 has a temperature
T.sub.J=27.degree. C., and the ambient air likewise has a
temperature T.sub.U=27.degree. C. Due to the different
temperatures, temperature layerings form and the light beams 11,
which were originally parallel, are deflected towards the optically
denser medium, i.e. in the direction of the cooler medium. Since
the sheet in FIG. 4 is cooler than the ambient air, the light beams
11 are deflected in the direction of the sheet 9 and the edge of
the sheet 9 is measured too low. This means that the distance of
the sheet 9 may already have fallen below the required safety
distance although the CCD line sensor 6 measures an acceptable
distance due to the deflection of the light beams 11.
The sheet grippers 13 on the jetting cylinder 17 are visible in
FIG. 5. They have a comparatively high temperature T.sub.G of
31.degree. C. The jetting cylinder 17 and the ambient air again
have the same temperature of 27.degree. C. This causes the position
of the grippers 13 on the jetting cylinder 17 to be measured too
high due to the higher temperature, and causes the computer 15 to
wrongly deduce that the threshold is exceeded, resulting in an
unnecessary switching-off of the printing process. FIG. 5
additionally shows a temperature sensor 14 for sensing the
temperature T.sub.G of the grippers 13. It is to be understood that
there may be multiple temperature sensors 14 to measure the
temperature T.sub.G of all of the grippers 13 over the entire width
of the machine. In addition, FIG. 5 shows a temperature control
device 16 for influencing the temperature of the jetting cylinder
17. Such a temperature control device 16 is capable of heating and
cooling to modify the temperature of the jetting cylinder 17. In
this way, thermal effects may be reduced by adapting the
temperature of the jetting cylinder 17 to the temperature of the
grippers 13, for example.
FIG. 5A illustrates how the thermal influence changes the
development of the intensity 10 on the CCD line sensor 6 in a
characteristic and reproducible way. The graphs of FIG. 5A indicate
the deflection caused by a cold measured surface. Since the
influence is reproducible, characteristic values of the curve may
be found. They may be used to predict the temperature and to deduce
the actual position of the edge of the sheet 9. For this purpose,
the computer 15, for instance, compares the height difference
between the first local maximum of the uninfluenced intensity
pattern 10 saved on the computer 15 and shown in FIG. 3 and the
first local maximum of the intensity pattern 10 measured under
thermal influences. This may potentially require a filtering and
smoothing of the curve by the computer 15. The difference between
the first local maximums is clearly positive without thermal
influences but negative in the case of a cold surface. In this way,
the computer 15 may effect temperature compensation, allowing sheet
edges of the sheet 9 to be measured and detected irrespective of
thermal influences within a certain temperature range. This
prevents the printing machine 1 from being unnecessarily switched
off and increases the productivity of the machine.
In FIG. 6, a cover plate 12 is additionally disposed in front of
the receiver 5. This cover plate 12 is used to eliminate the
spatial region of steep temperature gradients, preventing them from
reaching the CCD line sensor 6 and thus preventing strongly
deflected light beams 11 from being evaluated. However, the cover
plate 12 needs to be manually or automatically adjusted as a
function of the thickness of the sheet 9 that is used. If the cover
plate 12 is adjustable in an automated way, the computer 15 makes
the adjustment as a function of the input or recognized printing
material.
* * * * *